28,456 research outputs found
The stratigraphical distribution of Mid-Cretaceous foraminifera near Ventor, Isle of Wight
Ventnor No. 2 Borehole, located near Ventnor, Isle of Wight, penetrated the basal part of the Chalk Group and the Selborne Group before terminating in the upper part of the Lower Greensand Group (Sandrock Formation). The borehole was examined for Foraminifera, and although they were not seen in the Sandrock Formation and Monks Bay Sandstone Formation, the remainder of the borehole yielded moderately low diversity assemblages dominated by agglutinated species. Foraminiferal zones 3–6 (H dentatus to M. fallax/M. rostratum macrofaunal zones) were identified in the Gault Formation and zones 6 (lower) to 6a (M. fallax/M. rostratum to A. briacensis macrofaunal zones) were identified in the Upper Greensand Formation. Assemblages from the overlying West Melbury Marly Chalk Formation were used to identify foraminiferal zones BGS1-BGS3 (M. mantelli and M. dixoni macrofaunal zones)
Star clusters as building blocks for dSph galaxies formation
We study numerically the formation of dSph galaxies. Intense star bursts,
e.g. in gas-rich environments, typically produce a few to a few hundred young
star clusters, within a region of just a few hundred pc. The dynamical
evolution of these star clusters may explain the formation of the luminous
component of dwarf spheroidal galaxies (dSph). Here we perform a numerical
experiment to show that the evolution of star clusters complexes in dark matter
haloes can explain the formation of the luminous components of dSph galaxies.Comment: 4 pages, 4 figures, Proceedings of IAU symposium 266 'Star Clusters -
Basic Building Blocks
The Quantum-Classical Crossover in the Adiabatic Response of Chaotic Systems
The autocorrelation function of the force acting on a slow classical system,
resulting from interaction with a fast quantum system is calculated following
Berry-Robbins and Jarzynski within the leading order correction to the
adiabatic approximation. The time integral of the autocorrelation function is
proportional to the rate of dissipation. The fast quantum system is assumed to
be chaotic in the classical limit for each configuration of the slow system. An
analytic formula is obtained for the finite time integral of the correlation
function, in the framework of random matrix theory (RMT), for a specific
dependence on the adiabatically varying parameter. Extension to a wider class
of RMT models is discussed. For the Gaussian unitary and symplectic ensembles
for long times the time integral of the correlation function vanishes or falls
off as a Gaussian with a characteristic time that is proportional to the
Heisenberg time, depending on the details of the model. The fall off is
inversely proportional to time for the Gaussian orthogonal ensemble. The
correlation function is found to be dominated by the nearest neighbor level
spacings. It was calculated for a variety of nearest neighbor level spacing
distributions, including ones that do not originate from RMT ensembles. The
various approximate formulas obtained are tested numerically in RMT. The
results shed light on the quantum to classical crossover for chaotic systems.
The implications on the possibility to experimentally observe deterministic
friction are discussed.Comment: 26 pages, including 6 figure
A Green's function approach to the natural vibration of thin spherical shell segments - A numerical method Final report
Green function approach to natural vibration of thin spherical shell segment
A Possible Formation Scenario for Dwarf Spheroidal Galaxies - II: A Parameter Study
Dwarf spheroidal (dSph) galaxies are considered the basic building blocks of
the galaxy formation process in the LCDM (Lambda Cold Dark Matter) hierarchical
cosmological model. These galaxies are believed to be the most dark matter (DM)
dominated systems known, have the lowest stellar content, and are poor in gas.
Many theories attempt to explain the formation of dSph galaxies resorting to
the fact that these galaxies are mainly found orbiting large galaxies or
invoking other mechanisms of interactions. Here we show the full set of
simulation as an extension of our fiducial model, where we study the formation
of classical dSph galaxies in isolation by dissolving star clusters within the
DM halo of the dwarf galaxy. In our parameter survey we adopt cored and cusped
DM halo profiles and consider different numbers of dissolving star clusters. We
investigate the dependency of observable quantities with different masses and
scale-lengths of the DM halo and different star formation efficiencies (SFE).
We find that our proposed scenario explains many features of the classical dSph
galaxies of the Milky Way, like their morphology and their dynamics. We see
trends how the surface brightness and the scale-length of the luminous
component vary with the parameters of our simulations. We also identify how
irregularities in their shape, i.e. clumpiness and ellipticity vary in our
simulations. In velocity space, we identify the parameters leading to flat
velocity dispersions curves. We recognize kinematically cold substructures in
velocity space, named fossil remnants and stemming from our unique initial
conditions, which alter the expected results. These streaming motions are
considered as a key feature for future observation with high resolution to
validate our scenario.Comment: 23 pages, 9 figures, 4 Tables, accepted for publication in MNRA
ARCS, The Arcminute Radio Cluster-lens Search - I. Selection Criteria and Initial Results
We present the results of an unbiased radio search for gravitational lensing
events with image separations between 15 and 60 arcsec, which would be
associated with clusters of galaxies with masses >10^{13-14}M_{\sun}. A parent
population of 1023 extended radio sources stronger than 35 mJy with stellar
optical identifications was selected using the FIRST radio catalogue at 1.4 GHz
and the APM optical catalogue. The FIRST catalogue was then searched for
companions to the parent sources stronger than 7 mJy and with separation in the
range 15 to 60 arcsec. Higher resolution observations of the resulting 38 lens
candidates were made with the VLA at 1.4 GHz and 5 GHz, and with MERLIN at 5
GHz in order to test the lens hypothesis in each case. None of our targets was
found to be a gravitational lens system. These results provide the best current
constraint on the lensing rate for this angular scale, but improved
calculations of lensing rates from realistic simulations of the clustering of
matter on the relevant scales are required before cosmologically significant
constraints can be derived from this null result. We now have an efficient,
tested observational strategy with which it will be possible to make an
order-of-magnitude larger unbiased search in the near future.Comment: Accepted for publication in MNRAS. 12 pages, 29 included PostScript
figure
Band Distributions for Quantum Chaos on the Torus
Band distributions (BDs) are introduced describing quantization in a toral
phase space. A BD is the uniform average of an eigenstate phase-space
probability distribution over a band of toral boundary conditions. A general
explicit expression for the Wigner BD is obtained. It is shown that the Wigner
functions for {\em all} of the band eigenstates can be reproduced from the
Wigner BD. Also, BDs are shown to be closer to classical distributions than
eigenstate distributions. Generalized BDs, associated with sets of adjacent
bands, are used to extend in a natural way the Chern-index characterization of
the classical-quantum correspondence on the torus to arbitrary rational values
of the scaled Planck constant.Comment: 12 REVTEX page
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